1. Field of the Invention
The present invention relates to a nano-sized palladium-doped anion exchange resin catalyst or palladium-doped cation exchange resin catalyst, a preparation method thereof and a method of removing dissolved oxygen in water using the same.
2. Description of the Related Art
Dissolved oxygen (DO) is regarded as an important factor that influences water pollution and eutrophication and also determines the successes or failure of biochemical wastewater treatment, microbial culture, the production of semiconductors, food and pharmaceuticals, and the fermentation industry, and thus, techniques for removing DO present in service water are receiving increased attention.
Generally, service water dissolves oxygen from air when in contact with air and thus contains DO of about 8˜10 ppm at room temperature. Although the amount of DO present in water at room temperature is not high, when DO-saturated water is used in nuclear power plant systems, it causes the corrosion of metal material for systems and shortens the life span of equipment. As well, the case where an excess of a corrosion product is attached to a heat transfer surface at high temperatures decreases process heat efficiency and entails the danger of explosions and unexpected shutdowns. Hence, in the steam generator system of a nuclear power plant, in order to minimize the corrosion of metal material by DO, the water quality standard for a DO concentration is strictly regulated to about 7˜10 ppb.
Semiconductor production is another process in which the product quality is greatly affected by the DO content of service water. Ultrapure water for use in semiconductor production is used as cleaning water after etching of a silicon wafer. As such, in the case where DO is present in semiconductor-cleaning water, even if the concentration thereof is very low, an oxide film spontaneously forms on the surface of a semiconductor device, undesirably deteriorating the device performance. Therefore, with the intention of fabricating semiconductor devices having high quality, there is a need to develop techniques for diminishing the amount of DO in semiconductor-cleaning water. As the degree of integration of semiconductors is increased, the quality of ultrapure water is also required to increase.
Methods of removing DO from industrial water are necessary to ensure the safety and efficiency of the process using ultrapure water as service water and improve the quality of semiconductor products that are exported from Korea, and thus technical research and development therefor is required.
Conventional methods of removing DO in water include mechanical deaeration, reducing agent treatment, and membrane treatment.
The mechanical deaeration method is classified into vacuum deaeration and heat deaeration. The vacuum deaeration method has been mainly employed to date in order to eliminate DO from service water for the steam generator of a nuclear power plant, and the operation principle thereof is to spray service water from the upper portion of a packing column in a vacuum to decrease the partial pressure of gas in the column, thereby eliminating non-condensable gases containing oxygen gas.
The service water treated typically through the vacuum deaeration method is known to contain DO at a concentration ranging from 30 to 40 ppb, but actually contains DO at a concentration higher than the above range due to the inflow of air to a sealing device. Further, a specific sealing device is required in order to maintain the system in a vacuum state, and furthermore, to maintain the vacuum state in the packing column, high device cost and maintenance costs are incurred.
In the heat deaeration method, because gas solubility in water is proportional to the partial pressure of that gas in a gas phase according to Henry's Law, dissolved gas in an aqueous solution may be removed by decreasing the partial pressure of a gas in a gas phase. This method is able to decrease the DO concentration in water to less than 7 ppb through optimal operation of the heat deaerator, but is impossible to apply to a place lacking a steam heat source.
In addition, one effective method for removing DO in water is the use of a reducing agent such as hydrazine. As represented by Reaction 1 below, hydrazine reacts with DO in water, thus producing nitrogen gas and water molecules. Because the nitrogen gas and water molecules, which are products of such a chemical reaction, do not affect the corrosion of metal material, the above method is widely utilized to remove DO.N2H4+O2→N2+2H2O  Reaction 1
However, the method of removing DO using the reducing agent suffers because the reaction should be conducted only at high water temperatures of at least 80° C., and thus DO is difficult to remove at room temperature, consequently increasing energy consumption, and further, unreacted reducing agent acts as a secondary pollutant.
In addition, Korean Patent No. 595529 discloses a porous membrane which has high porosity and a polar surface by adding a specific amount of alumina through a phase transfer process, and which is doped with a predetermined amount of transition metal selected from among palladium and platinum. The porous membrane is advantageous because the loss of transition metal is lower compared to conventional methods, and hydrogen gas is efficiently supplied through the pores of the porous membrane, thus ensuring process stability. However, the porous membrane brings about low DO removal efficiency of 65%, and therefore, the use thereof is limited in removing DO from service water for semiconductors and power plants requiring high DO removal efficiency.